The present invention relates generally to air conditioners and heat pumps and methods to control humidity of conditioning air.
To warm and humidify indoor air in cold environment heat pumps, electrical or gas heaters in combination with devices injecting sprayed water in air are widely used. Also for humidification of indoor air in residential and commercial buildings different types of portable humidifiers can be used.
In hot climate air conditioners are used to cool and dehumidify air. In air conditioners air flowing through an evaporator rejects heat to the evaporating coil and simultaneously condenses moisture on the heat transfer surface of the same coil. However, in high ambient humidity, dehumidification by air conditioners is often not sufficient.
For residential and small commercial systems the most popular way of dehumidification requires installation of a dehumidifier in addition to an air conditioner. In the US the sale of portable dehumidifiers exceeds 1,000,000 each year. The dehumidifier gives consumers an advantage to control independently both parameters of indoor air: temperature and relative humidity. A thermostat controls the operation of the air conditioner depending on the room temperature and a humidistat controls the operation of the dehumidifier depending on the humidity in the room. However, this technology consumes an excessive amount of energy. First, the dehumidifier itself consumes energy to run both a compressor and a fan. Second, unlike an air conditioner where the condenser rejects heat to the ambient, in a dehumidifier the combined energy of both the compressor and the fan goes back to the room. To offset an influx of this energy the air conditioner should have extra capacity and spend extra energy.
Several attempts have been made to achieve sufficient dehumidification of conditioned air without an extra dehumidifier. Some designers use oversized air conditioners to reduce the evaporating temperature and increase moisture condensation. However, relative humidity of air leaving an oversized air conditioner may reach from 95% to 100% with the temperature below the comfortable level.
The best alternative is to use a properly sized air conditioner to cool and dehumidify indoor air. Moisture condensation depends mainly on the temperature of the evaporator heat transfer surface. Reduction in the size of the evaporating surface can reduce the evaporating temperature and increase moisture condensation. It is widely recognized, however, that smaller evaporating coil and lower evaporating temperature of refrigerant result in lower efficiency and capacity of the air conditioner. Thus, small evaporators reduce efficiency and capacity, while enlarging of the evaporators can lead to excessive relative humidity that, in turn, causes damp and mould in the room.
Some designers use a method that involves heat pipe technology. See, for example, U.S. Pat. Nos. 5,333,470 and 5,448,897. Such design adds two additional heat exchangers to the evaporator: one is a xe2x80x9cprecoolingxe2x80x9d coil upstream of the evaporator, another is a xe2x80x9creheatingxe2x80x9d coil downstream of the evaporator. Two coils are filled with phase change medium and connected to each other the way that the coil upstream of the evaporator picks heat from the incoming air and pumps this heat to the coil downstream of the evaporator and to outgoing air. Thus, the temperature of incoming air and the temperature of the heat transfer surfaces of the evaporator are decreased, which causes additional condensation and reduction in absolute humidity of air. Because the heat from incoming air increases the temperature of air exiting the coil downstream of the evaporator, relative humidity of air that exits the conditioner is reduced considerably. However, installation and operation of heat pipes generally involve notable expenses. In addition, such systems lead to an excessive pressure drop in air stream because there are two extra heat exchangers. In case there is no need for relative humidity reduction there is some extra complication involved in disabling of the heat pipe.
U.S. Pat. No. 3,469,353 discloses an air conditioner capable to work in the conventional and the dehumidification modes. To provide the air conditioner with dehumidification abilities the system has two outside coils, two inside coils and two capillary tubes (expansion devices). In the cooling mode refrigerant condenses in both outside coils, expands in the first capillary tube and evaporates in both inside coils. In the dehumidification mode refrigerant partly condenses in the first outside coil, then flows to the second inside coil and fully condenses there. Then liquid refrigerant expands in the second capillary tube and evaporates in the first inside coil. The cold air leaving the first inside coil goes to the second inside coil that works now as a condenser and warms up there reducing the relative humidity. Second outside coil that works as a condenser in the cooling mode in the dehumidification mode is idle. The main problem of this design is low energy efficiency. The use of the second inside coil as a condenser does not increase the cooling capacity and brings extra heat to conditioning air.
There is also a solution involving the subcooling technology. See, for example, U.S. Pat. No. 6,212,892. In the design of U.S. Pat. No. 6,212,892 an auxiliary coil is installed in an air passage downstream of the evaporator. In the dehumidification mode hot liquid refrigerant leaving the condenser expands in a pressure reduction device, then flows to an auxiliary coil that works as a subcooler rejecting heat from refrigerant to air cooled in the evaporator. After being in the auxiliary coil refrigerant goes to an expansion device and then to the evaporator. In the evaporator liquid refrigerant evaporates absorbing heat from air. Since refrigerant is preliminary subcooled, capacity of the evaporator increases and the temperature of its heat transfer surface goes down. Much like with the heat pipe technology, it causes additional condensation and reduction in absolute humidity of air. Because the temperature of air exiting the subcooling coils after the evaporator is increased, relative humidity of air is further reduced. This design is relatively simple and can provide equal or even better dehumidification as provided in air conditioners with heat pipes. When desirable humidity level is achieved, air conditioner works in a conventional cooling mode. A valve directs refrigerant flow that was liquefied in the condenser to an expansion device and after it expands there it directs it to the auxiliary coil that now works as a part of the evaporator. The temperature of air leaving the air conditioner in the conventional mode is lower and relative humidity is higher. Alternation of conventional and dehumidification modes can provide desirable level of humidity and temperature in the room. However, the system requires more refrigerant in the dehumidification mode than in the conventional cooling mode. Reduced refrigerant charge may reduce capacity and moisture condensation in the dehumidification mode, while excessive amount of refrigerant can cause an increase in the condensing temperature and efficiency in the conventional mode. To overcome this, a receiver may be installed. Still, the efficiency of the air conditioner in the conventional cycle, especially with a capillary tube or a short tube restrictor, can be lower than in the traditional design.
One preferred embodiment of the invention provides a climate control system with an air conditioner or a heat pump for conditioning air. The system includes a compressor for compressing gaseous refrigerant, a condenser for condensing refrigerant exiting the compressor, an expansion device to expand liquid refrigerant in both directions, an evaporator for evaporating liquid refrigerant after the expansion device, an auxiliary coil for either subcooling or evaporating liquid refrigerant, valve means to direct refrigerant flow leaving the condenser either to the expansion device to absorb heat from conditioning air by refrigerant in the auxiliary coil or to the auxiliary coil to reject heat to the air from refrigerant in the auxiliary coil, a refrigerant line connecting the auxiliary coil and the expansion device, a refrigerant line connecting the auxiliary coil and the valve means, refrigerant communication means to connect the valve means and the expansion device and to store extra amount of liquid refrigerant at the time when the auxiliary coil absorbs heat from conditioning air; a fan for moving air to be conditioned against the evaporator and against the auxiliary coil, and control means to control the operation of the compressor and the fan and the position of the valve means.
Further in accordance with the present invention, a four-way reversing valve as the valve means is provided.
In accordance with another aspect of the invention, the system further comprises a restrictor positioned in the refrigerant line that connects the valve means and the auxiliary coil. The restrictor expands refrigerant in one direction and allows a free pass in the other direction.
In accordance with yet another aspect of the invention, the refrigerant communication means further consist of tubing and an auxiliary volume to accommodate an extra amount of liquid refrigerant.
In accordance with yet another aspect of the invention the system further comprises heating means to operate in a heating mode and a humidification device to humidify indoor air.
In the several embodiments of the invention, the control means include a thermostat, a humidistat, and an evaporator surface temperature sensor to control the valve means and the system operation. Depending on the thermostat and the humidistat settings and on the condition of air the system is either in operation or off. While the system is in the cooling or the dehumidification operations, the valve means direct refrigerant flow to either absorb heat by refrigerant from conditioning air in the auxiliary coil or to reject heat to the air from refrigerant in the auxiliary coil. The evaporator temperature sensor shows when the temperature of the evaporator surface drops below some predetermined level. To prevent building of ice on the surface control means either redirect the refrigerant flow with the valve means or turn off the compressor. In the heating mode the control means control operations of the heating means and the humidification device.
Another preferred embodiment of the invention provides a climate control system with an air conditioner or a heat pump for conditioning air. The system comprises a compressor for compressing gaseous refrigerant, a condenser for condensing refrigerant after exiting the compressor, an expansion device to expand liquid refrigerant in both directions, an evaporator for evaporating liquid refrigerant after the expansion device, an auxiliary coil either for subcooling or for evaporating liquid refrigerant, valve means to direct refrigerant to the auxiliary coilxe2x80x94either to absorb heat from conditioning air by refrigerant in the auxiliary coil or to reject heat to conditioning air from refrigerant in the auxiliary coil, a receiver to accommodate a part of liquid refrigerant at the time when the auxiliary coil absorbs heat from conditioning air; a fan for moving air to be conditioned against the evaporator and against the auxiliary coil, control means to control the operation of the compressor and the fan and to control the position of the valve means.
In accordance with yet another aspect of the invention, the valve means is a four-way valve.
In another embodiment of the present invention, a method for cooling and dehumidification of air using an air conditioning and heat pump system is provided. The system includes a refrigerant circuit and an air circuit. The refrigerant circuit consists of a compressor, a condenser, an expansion device, refrigerant communication means between the condenser and the expansion device, an auxiliary coil, an evaporating coil, and valve means to direct refrigerant flow after the condenser either to the auxiliary coil or to the expansion device and to direct refrigerant flow after the auxiliary coil either to the expansion device or to the evaporating coil. The air circuit includes a fan moving air to be conditioned.
Operation in the cooling mode comprises of the steps of compressing gaseous refrigerant in the compressor, condensing refrigerant in the condenser, flowing liquid refrigerant through the refrigerant communication means to the expansion device, expanding refrigerant in the expansion device, flowing refrigerant to the auxiliary coil, partially evaporating refrigerant in the auxiliary coil to cool the coil and passing air, flowing partially liquid, partially vapor refrigerant to the evaporating coil, completely evaporating refrigerant in the evaporating coil to cool the evaporating coil and passing air, flowing vaporized refrigerant to the compressor; moving a stream of warm air against the evaporating coil and against the auxiliary coil to cool the air.
Operation in the dehumidification mode comprises of the steps of compressing gaseous refrigerant in the compressor, condensing refrigerant in the condenser, flowing liquid refrigerant to the cooled auxiliary coil, subcooling refrigerant in the auxiliary coil and warming passing air, flowing subcooled liquid refrigerant after the auxiliary coil to the expansion device, expanding refrigerant in the expansion device, flowing refrigerant to the evaporating coil, evaporating refrigerant in the evaporating coil and cooling and dehumidifying passing air, flowing vaporized refrigerant to the compressor; moving the stream of warm air against the evaporating coil to cool and dehumidify the air stream, moving cooled and dehumidified stream of air against the auxiliary coil to subcool liquid refrigerant and to warm the air stream.